1. Field of the Invention
The present invention relates to a method and apparatus useful for evaluation of catalysts. More particularly, the present invention is directed to simulating poisoning and deactivating catalysts with catalyst poison compounds at least one catalyst poison compound selected from the group consisting of a compound comprising phosphorous, a compound comprising zinc compound and a compound comprising phosphorous and zinc.
2. Description of the Related Art
The art discloses that additives such as lubricants used in internal combustion engine oils can contain compounds which contain phosphorous and/or zinc. Such compounds include materials such as zinc dialkyldithiophosphate also referred to as zinc dithiophosphate (ZDTP) and zinc dithiocarbamate (ZDTC). Other disclosed zinc and phosphorous additives to oil include metallic detergents including phosphorares and phosphorous compounds included as extreme pressure agents. Reference is made to U.S. Pat. Nos. 4,674,447 and 5,696,065 and European Application No. 95309415. The phosphorous and zinc are disclosed to lower the function of the motor vehicle exhaust treatment catalyst.
As engine technology and exhaust gas treatment technology has improved engines pass less lubricating oil, including phosphorous and zinc compound to the catalysts and the catalysts have been sufficiently active to treat exhaust gases in accordance with various government regulations. However, as engine performance continues to increase and environmental regulations become more stringent catalysts activity will have to be increased and maintained with longer engine life. As engine life increases there will be a greater build up of compounds, particularly phosphorous and/or zinc compounds passing to the emission treatment catalyst from the engine. It is desirable to have a method to simulate the poisoning of the catalyst poisoning and deactivation in the laboratory for different engine systems run at different conditions to for various reasons including to more rapidly screen new catalysts.
Numerous methods have been used in the past to simulate long term deactivation of a catalyst, using an engine bench test. Most of these methods involve running an engine at very high speed and load conditions cyclically for several hours, often creating a large exotherm in the catalyst bed during certain portions of the test cycle. These adverse conditions deactivate the catalytic converter, and a correlation is drawn between this type of rapid aging cycle and on-road deactivation of the emission control system in general, and catalytic converter, in particular. While such correlations can be developed, they do not always mimic the actual deactivation modes, such as poison accumulation.
References such as U.S. Pat. No. 4,771,029 disclose the ad recognition of catalyst poisoning by materials such as phosphorous. U.S. Pat. No. 4,727,746 discloses a modal mass analysis method for simulating driving conditions for evaluating exhaust gases.
Ueda et al., Engine Oil Additive Effects on Deactivation of Monolithic Three-Way Catalysts and Oxygen Sensors, SAE, SP-1043, 1994, discloses that it is widely known that ZDTP results in phosphorous poisoning of three-way emissions catalysts. Catalysts and oxygen sensors were xe2x80x9cpoisonedxe2x80x9d on the engine bench by test oils, varying the quantity of phosphorous and ash. The performance of the catalysts and sensors was evaluated using a FTP test on a chassis dynamometer. It was found that calcium and magnesium helped prevent the phosphorous from adhering to the catalyst.
Joy et al., The Influence of Sulfur Species on the Laboratory Performance of Automotive Three Component Control Catalysts, SAE, 1979, discloses that poisons such as phosphorous and sulfur poison catalysts. Studies were done in the laboratory on the effects of sulfur dioxide.
Baba et al., Numerical Simulation of Deactivation Process of Three-way Catalytic Converters, SAE, SP-1533, Mar. 6, 2000, discloses a numerical simulation method to predict the deactivation process of three-way catalytic converters. Based on simulated results of the deactivated state inside the bench aged catalysts, which are noble metal particle size and catalyst activity distributions, thermal responses and light-off behaviors during warm-up tests are predicted.
Natoli et al., Three-way Catalyst Deactivation by Lubricants During Fast Aging Engine Tests, Gionale ed Atti della Associazione Technica dell""Automobile, Vol. 48, No. 12, p 685, 1995 discloses that engine lubricants play an important role in poisoning three-way catalytic converters. The objective was to reproduce in the laboratory the aging of the catalysts under accelerated conditions in order to evaluate the influence of additive contained in engine oils.
Ball et al., Application of accelerated Rapid Aging Test (RAT) Schedules with Poison: The Effects of Oil Derived Poisons, Thermal Degradation and catalyst Volume on FTP Emissions, SAE, SP-1296, 43-53, 1997 discloses dynamometer rapid aging tests incorporate both thermal and oil-derived poison degradation are used to age catalysts for FTP emissions studies. Vehicle aged converters are analyzed to determine the axial aged phosphorous distribution throughout the catalyst. These profiles are compared to dynamometer aged RAT aged catalysts.
Other references of interest include: Carol et al., High temperature Deactivation of Three-way Catalyst, SAE, 1989; Pattas et al., Computer Aided Assessment of Catalyst Aging Cycles, SAE, 1995. Beck et al., Impact of Oil-derived Catalyst Poisons on FTP Performance of LEV Catalyst Systems, SAE, SP-1296, 1-10, 1997. Jobson et al., Deterioration of Three-way Automotive Catalysts, SAE, SP-957, 153-66, 1993; and Williamson et al., Effects of Oil Phosphorous on Deactivation of Monolithic Three-way Catalysts, Appl. Catal. (1985), 15(2), 277-92.
Automotive catalytic converters and filters comprise at least one catalyst composition. Such catalyst compositions are susceptible to poisoning due to lubricant oilxe2x80x94derived phosphorus, zinc, sulfur and other compounds. Catalyst compositions (referred to as xe2x80x9ccatalystsxe2x80x9d) can be coated on to a suitable substrate. The coated catalyst when applied to the substrate in a slurry or liquid form is also referred to as a xe2x80x9cwashcoatxe2x80x9d. The poisons may accumulate on the surface of the washcoat, creating a physical barrier, or they may interact with the catalytic material in the washcoat, resulting in loss of catalytic activity, and/or become a barrier to particulate filters such as foam, screens and wallflow filters. The poison level and type can vary, depending upon the design of the engine and the operating conditions. In the development of the emission control system, it is critical to know the type of poison a exposure and the impact of poison on the emissions control system in general, and the catalytic converter, in particular.
The present invention relates to a method and apparatus that effectively duplicates these poisoning conditions in a laboratory environment. In addition, the invention relates to a method and apparatus that duplicates, on an engine test stand, the equivalent of extended on road-type poison exposure, deposition and catalyst deactivation and/or filter clogging.
It is generally known that lubricant-derived phosphorus, zinc and sulfur can accumulate on the catalyst surface and result in deactivation. This poisoning mechanism is quite complex, and highly dependent upon the operating temperature, the oil consumption of the engine, and the source of the oil consumption. For example, when oil leaks past the piston rings, and washes into the combustion chamber, it goes through the combustion process. This will result in certain types of phosphorus and/or zinc compounds (among other contaminants). Particular compounds may have a certain type of deactivation effect on the catalytic converter, depending upon the operating condition. On the other hand, oil that leaks past the exhaust valve guide and stem, may not go through the combustion process, and result in a different type of poisoning of the catalytic converter.
Numerous methods have been used in the past to simulate long term deactivation of a catalyst, using an engine bench test. Most of these methods involve running an engine at very high speed and load conditions cyclically for several hours, often creating a large exotherm in the catalyst bed during certain portions of the test cycle. These adverse conditions deactivate the catalytic converter, and a correlation is drawn between this type of rapid aging cycle and on-road deactivation of the emission control system in general, and catalytic converter, in particular. While such correlations can be developed, they do not always mimic the actual deactivation modes, such as poison accumulation. In this invention, a method has been developed to accelerate the catalyst aging process, with poison deposition on an emission treatment device which are typically a catalyst and/or a filter. The catalyst can be a catalyst composition in self supported form such as a powder, pellet or other form article, or in a supported form wherein the catalyst composition is supported on a suitable substrate such as a monolithic article which can be a metallic or ceramic flow through or wall flow honeycomb, wire mesh and ceramic foam.
In accordance with the method of the present invention, an emission treatment device selected from at least one of a catalyst and a filter, is combined with at least one poison compound having at least one component selected from the group consisting phosphorous, zinc and sulfur to form a poisoned emission treatment device.
The poisoned emission treatment device is heated at suitable temperatures, typically from about 200xc2x0 C. to about 1100xc2x0 C., preferably from about 300xc2x0 C. to about 800xc2x0 C., more preferably from about 300xc2x0 C. to about 500xc2x0 C., most preferable about 400xc2x0 C. for a sufficient time to calcine poisoned device. Typically the calcination time is from about 0.5 hours to about 24 hours preferably from about 1.0 hours to about 12 hours, more preferably from about 2.0 hours to about 8.0 hours, most preferable from about 3.0 hours to about 6.0 hours to form a calcined emission treatment device. The activity of the calcined emission treatment device can then be evaluated. The evaluation can include evaluating catalytic activity of an exhaust treatment catalyst to determine the conversion percent of at least one pollutant component by the catalyst, the light-off temperature of at least one pollutant component at a catalyst, and/or the efficiency of a filter.
In a specific embodiment, accordance with the method of the present invention the emission treatment device can be combined with poisons provided by a the operation of a gasoline or diesel engine, having an exhaust gas outlet or an exhaust gas manifold outlet. The engine can be on a bench stand in the laboratory or on a motor vehicle. An exhaust gas stream comprising pollutants selected at least one pollutant component selected from the group consisting of carbon monoxide, hydrocarbons and nitrogen oxides, volatile organic components and dry soot, from the exhaust gas outlet or the exhaust gas manifold outlet of the engine is passed to the emission treatment device. At least one poison compound having at least one component selected from the group consisting phosphorous, zinc and sulfur can be added to the exhaust gas stream at a location between the exhaust gas outlet or the exhaust gas manifold outlet and the emission treatment device. The exhaust gas containing the poison compound can then contact the emission treatment device to form a poisoned emission treatment device. The emission treatment device can then be evaluated.
In another specific embodiment the gasoline or diesel engine have an oil pan in which lubricating oil is located. At least one poison compound having at least one component selected from the group consisting phosphorous, zinc and sulfur is added to the oil in an amount in excess of the amount functionally required for the oil to function. The emission treatment device can then be evaluated.
In an alternative and preferred embodiment, the emission treatment device can be combined with at least one poison compound or precursor compound having at least one component selected from the group consisting phosphorous, zinc and sulfur. The poison or poison precursor can be applied directly to the emission treatment device. The device can then be calcined. Where the device is a filter or catalyzed substrate the poison or poison precursor can be coated with a solution or slurry, sprayed, or deposited by other suitable methods. The poisoned device can then be evaluated. In preferred embodiments, catalyzed substrates are coated with a slurry containing the poison or poison precursor. The coated substrate can be calcined, if necessary, and then evaluated. This provided a rapid way to screen the effect of poisons on various catalyst compositions. The method is particularly useful to evaluate the catalysts useful as gaseous emissions exhaust catalyst. Such catalysts typically are used to treat at least one pollutant component selected from the group consisting of carbon monoxide, hydrocarbons and nitrogen oxides, volatile organic components and dry soot.
In an alternative embodiment the emission treatment device (e.g., the catalyst) to be aged is mounted on an engine test bench. The lubricating oil in the engine may be doped with high levels of catalyst poison or poison precursor such as zinc dialkyl dithiophosphate (ZDDP), a commercially available phosphorus/Zinc/Sulfur compound. Alternatively or in combination, an apparatus can be set up to inject ZDDP-containing engine oil directly into the exhaust stream, ahead of the catalytic converter. The level of ZDDP and the amount of oil injected can be varied, depending upon the degree of deactivation required. The engine can then run through a combination of high speed and load (to thermally deactivate the catalyst), and low speed/low load conditions combined with injection of the oil into the exhaust stream (to deposit the poisons on the catalytic surface). This combination of high and low temperature operation is run cyclically or sequentially, until the desired level of deactivation is achieved. In general, exhaust gas temperatures during accelerated aging on an engine dynamometer or a laboratory reactor can be vary, from about 300xc2x0 C. during low load and low speed operation, and up to about 1200xc2x0 C. during high load and high speed operation. More specifically, the exhaust gas temperatures can be vary, in the range of 300xc2x0 C. to 1200xc2x0 C. Alternatively, operating ranges can be from about 300xc2x0 C. to about 600xc2x0 C. during low speed and low load operation, or from about 600xc2x0 C. to about 1200xc2x0 C. during high speed and high load operation.
The present invention includes a method of introducing the poison-containing oil into the exhaust stream at the above conditions. The process of introducing engine lubricating oil (with or without elevated levels of poisonous compounds) is critical. For instance, if oil is dripped or injected into the exhaust stream, it could coke or oxidize at the point of introduction, and may 1) never reach the catalyst washcoat surface, or 2) coke and block the nozzle or other device used to drip or inject the oil into the exhaust stream.
In accordance with the method of the present invention, coking of oil in the process of accelerated aging of a catalytic converter on an engine dynamometer or a laboratory reactor is prevented or minimized. Forcing the oil in to the exhaust stream as a mist with the assistance of high pressure nitrogen or other inert gas is one embodiment of the present invention. This assists in keeping the flow nozzle clear during certain types of catalyst aging.
Another embodiment of this invention is the introduction of both high pressure nitrogen (or other inert gas) and water with the oil. The oil, water and nitrogen have to be introduced at predetermined rates and pressures, sufficient to keep a clear flow through the injection nozzle or orifice. This method results in the emulsification of the oil by the water. As the mixture comes in contact with the hot walls of the injector and tube, some coking will begin. However, the water in the emulsion evaporates at these temperatures, and thus cleans out the oil flow passage. This self-cleaning mechanism is preferred to keeping a continuous flow of oil into the exhaust gas stream for the entire duration of oil injection during certain arduous the accelerated aging test protocol.
The method and apparatus of the present invention are particularly useful when the emission treatment device comprises a catalyst supported on a substrate. In preferred embodiments the catalyst comprises a catalyst composition comprising a support; and at least one catalytic material selected from the group consisting of at least one platinum group metal component, gold and silver. The platinum group metal component can be selected from at least on component selected from the group consisting of platinum, palladium, rhodium, ruthenium and iridium.
The method is useful to evaluate the effect of poisons selected from the group of a compound comprising phosphorous, a compound comprising zinc compound, a sulfur compound, a compound comprising phosphorous and zinc, a compound comprising zinc and sulfur and a compound comprising phosphorous zinc and sulfur. Typically, the compounds comprising phosphorous are selected from the group consisting of ammonium hydrophosphate, phosphoric acid, phosphorus acid, and organo phosphorus compounds; compounds comprising zinc is selected from the group consisting of zinc oxide, zinc nitrate, zinc sulfate, zinc carbonate and organo zinc compounds; and the compound mixtures comprising phosphorous, and zinc can be selected from the group consisting of a mixture of zinc oxide and ammonium hydrophosphate, zinc dithio phosphate, and zinc phosphate.
Where the poison is added to the lubricating oil, it will be in excess of the amount typically in lubricating oil. The amount of poison or poison precursor is typically greater than about 0.15 weight percent of the oil and poison or poison precursor, and preferably from about 0.15 to 0.5, more preferably from 0.2 to 0.5 poison or poison precursor.
In a preferred method the compound mixture comprising phosphorous and zinc and optionally sulfur compounds is a in a slurry. A preferred mixture is an aqueous slurry of zinc oxide and ammonium hydrophosphate. The slurry is then coat applied, typically by coating or spraying on to a catalyst which is preferably a catalyst composition located on a substrate, on to a filter such as a wall flow filter. As necessary, and preferably the poisoned is calcined.
In typical evaluations the amount of the catalyst poison compound is from about 1.0 to about 20 weight percent of the catalyst.
The step of evaluating the catalytic activity of the gaseous emissions exhaust catalyst comprises contacting a synthetic gas comprising at least one pollutant component with the poisoned catalyst at predetermined conditions of temperature, time and pollutant component concentration to determine the conversion percent of at least one pollutant component and/or the light-off temperature of at least one pollutant component. The catalyst can have poison added at a predetermined rate. Catalyst light off is the temperature at which 50% conversion of a given pollutant is converted. This can be determined using flame ionization detector to measure hydrocarbon conversion. Carbon monoxide conversion can be measured using nondispersive infrared (NDIR) analysis. Nitrogen oxide conversion can be determined using a chemiluminescence analyzer.
Pressure drop, weight game, micro photographs can be used to assess the effect of poison as becoming a barrier to a filter.
The present invention further includes as an article, an emission treatment device selected from at least one of a catalyst and a filter. The emission treatment device has an over coat of a predetermined amount at least one poison or poison precursor compound having at least one component selected from the group consisting phosphorous, zinc and sulfur.
Where the article comprises an exhaust treatment catalyst. The catalyst comprises a composition having a support and at least one platinum group metal component selected from the group consisting of platinum, rhodium, ruthenium and iridium components.
In a specific embodiment the article comprises a catalyst supported on a substrate having channel extending from an inlet end to an outlet end and the poison is deposited in varying concentrations from the inlet to the outlet. The poison can be deposited in zones having different concentrations from the inlet to the outlet. The poison can be deposited in an inlet zone having a higher concentrations then an outlet zone located between the inlet zone and the outlet end.
The present application further includes an apparatus comprising a gasoline or diesel engine, having an exhaust gas outlet or an exhaust gas manifold outlet. There is an emission treatment device selected from at least one of a catalyst and a filter. A conduit communicates between the exhaust gas outlet or an exhaust gas manifold outlet and the emission treatment device. An overcoat on the catalyst composition has a predetermined amount of at least one poison compound or poison precursor having at least one component selected from the group consisting phosphorous, zinc and sulfur. There is feed port into the conduit at a location between the exhaust gas outlet or the exhaust gas manifold outlet and the emission treatment device; and a means to feed through the feed port at least one poison or a compound capable of forming the poison and having at least one component selected from the group consisting phosphorous, zinc and sulfur. There is a means to evaluate the emission treatment device to determine the conversion percent of at least one pollutant component by the catalyst, the light-off temperature of at least one pollutant component at the catalyst, and/or the efficiency of the filter.